1. Field of the Invention
The present invention is directed to an X-ray tube of the type having a cathode and an anode arranged in a vacuum housing, with an arrangement for magnetically deflecting the electron beam.
2. Description of the Prior Art
The possibility of deflecting the electron beam and the focal spot is of significance, particularly in computed tomography, since an improvement of the image quality can be achieved by the known measure of displacing the focal spot between two limit positions, thus doubling the data available for the calculation of the image of a body slice.
German OS 41 25 926 and European Application 0 460 421 disclose X-ray tubes of the type initially described.
In both of these known X-ray tubes, the arrangement for the deflection of the electron beam is formed by a deflection unit that is arranged outside the vacuum housing and includes a deflection coil. Arranging the deflection unit outside the vacuum housing yields the advantage that disadvantageous effects on the vacuum in the vacuum housing caused by the presence of the coil in the interior of the vacuum housing are avoided, for example the emission of gas by the insulation of the coil wire. Considerable electrical power must be supplied to the deflection units located outside the vacuum housing for effecting a specific deflection of the electron beam, so that an undesirably high amount of dissipated heat is released in conjunction with the deflection of the electron beam. This is a disadvantage in view of the thermal problems that already occur during operation of X-ray tubes.